Bump phpseclib/phpseclib in /libraries/google-api-php-client

Bumps [phpseclib/phpseclib](https://github.com/phpseclib/phpseclib) from 3.0.36 to 3.0.51.
- [Release notes](https://github.com/phpseclib/phpseclib/releases)
- [Changelog](https://github.com/phpseclib/phpseclib/blob/master/CHANGELOG.md)
- [Commits](phpseclib/phpseclib@3.0.36...3.0.51)

---
updated-dependencies:
- dependency-name: phpseclib/phpseclib
  dependency-version: 3.0.51
  dependency-type: direct:production
...

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Author: dependabot[bot]